Consecutive and reliable proton transfer channels construction based on the compatible interface between nanofiber and SPEEK

Abstract

It is indispensable to balance the proton conductivity and dimensional stability, as well as maintain the high long-term durability of proton exchange membranes (PEMs). Herein, we proposed the sandwich structure composite membrane containing a middle layer of sulfonated polyetheretherketone (SPEEK) sandwiched by two layers of hybrid polyimide (PI) nanofiber. The hybrid nanofibers were fabricated via in situ loading different contents of NH2-UiO-66 (NU6) onto PI nanofiber as proton acceptors for amino-functionalization, resulting in NU6@PI nanofibers (NP) with different forms of assembly. By incorporating three-dimensional nanofibers into SPEEK, the dimensional stability of the composite membrane was dramatically boosted. The –SO3H groups on SPEEK interact with –NH2 groups on NP to form long-range acid-base pairs and acid-rich layer along the NP-SPEEK interface, which can provide abundant proton-conducting sites for proton transfer. Significantly, the continuous and uniform assembly of NU6 on PI nanofiber can form a compatible interface with SPEEK, ensuring the reliability of the proton pathways and robust mechanical properties. Insufficient or excessive loads of NU6 will lead to an imperfect NP-SPEEK interface, resulting in discontinuous proton channels or forming numerous defects that hinder continuous proton transport. The composite membrane of 4NP-SPEEK-4NP (40%NU6@PI-SPEEK-40%NU6@PI) with consecutive and reliable proton transfer channels displays enhanced stress, optimal proton conductivity, and excellent H2/O2 fuel cell performance. The durability test at 60 °C and 100% RH for 32 days reveals that the proton conductivity retention and tensile strength of the composite membrane are 89.8% and 47.8 MPa, which are 33.8% and 52.7% higher than those of SPEEK, respectively. The prepared membranes not only can be potential candidates for fuel cells but also provides a useful strategy for the longtime effective construction and regulation of proton transport channels in PEMs.